1. Field of the Invention
The present invention relates to a process for preparing a polyarylene sulfide and, more particularly, to a process for preparing a granular polyarylene sulfide with a high yield and with efficiency while preventing a source of sulfur from decomposing during dehydration, a polyarylene sulfide having a high molecular weight and a high degree of whiteness and containing a salt within the polyarylene sulfide product in a lesser amount. The polyarylate sulfide is suitable for molding materials for various molded articles, films, sheets, and for varous injection moldings including mechanical, electric and electronic parts as well as IC sealants.
2. Description of Related Art
Polyarylene sulfides such as polyphenylene sulfides are thermoplastic while being partially thermosetting, and they have superior properties as engineering plastics, such as excellent resistance to chemicals, high mechanical strength over a broad temperature range, and good thermal rigidity.
Various processes for preparing polyarylene sulfides such as polyphenylene sulfides have been heretofore proposed.
For instance, U.S. Pat. No. 3,867,356 discloses a process in which a polyhalogen aromatic compound is reacted with an alkali metal hydrosulfide in an organic amide compound as a solvent in the presence of an alkali metal aminoalkanoate. This process, however, presents the problems that the resulting polyarylene sulfide has a low molecular weight and it is colored due to by-products produced by the side reactions between the polyhalogen aromatic compound and the alkali metal aminoalkanoate, thereby yielding no polyarylene sulfides with a high degree of whiteness.
U.S. Pat. No. 4,038,263 discloses a process in which a lithium halide is used as a catalyst in the reaction of p-dichlorobenzene with an alkali metal sulfide. This process, however, causes the alkali metal sulfide as a sulfur source to be decomposed during dehydration leading to lessening a production efficiency so that this process is industrially disadvantageous. The resulting polyphenylene sulfide is so colored that the product with a high degree of whiteness cannot be prepared. And the resulting product contains a relatively large amount of remaining salts. Furthermore, this process produces polymers in a yield as low as 70 to 85% so that improvements in yields have been demanded.